Synthesis of butadiene-derived polyolefin graft copolymers and their crystallization behaviors

Abstract

The ability to synthesize polyolefin-based copolymers with controlled chemical composition and chain microstructure provides great opportunities for their use in compatibilizing polyolefin blends, particularly including polyethylene (PE) and polypropylene (PP), to address their waste recycling challenges. In this study, polyolefin graft copolymers comprising semicrystalline PE side chain and amorphous polyethylethylene (PEE) backbone were synthesized by grafting amine-terminated 1,4-polybutadiene (PB) onto carboxyl-grafted 1,2-PB, followed by hydrogenation. A suite of characterization techniques were employed to assess the degree of functionalization, polymer microstructure, and molecular weight of these graft copolymers containing different side chain lengths and graft densities. Moreover, since most commodity polyolefins are semicrystalline, understanding the crystallization behavior of these polyolefin copolymers is important. Specifically, the non-isothermal crystallization behavior of these graft copolymers was investigated using differential scanning calorimetry (DSC) and the Jeziorny-modified Avrami model. Both the graft copolymers and their homopolymer grafts exhibited heterogeneous nucleation with predominantly one-dimensional crystal growth and similar overall crystallization rates. However, PEE-g-PE_10k and PEE-g-PE_5k showed opposite trends in activation energy, likely due to a competition between nucleation facilitation and crystal growth restriction introduced by the graft structure. A preliminary investigation indicates that the incorporation of these graft copolymers into mixed PE : PP (50 : 50) blends can lead to improved mechanical performance. This study reveals the impact of graft architecture on the crystallization behavior of polyolefin-based blend compatibilizers.